1. Technical Field
The invention relates to radio frequency (RF) receiver systems and measurements performed on same.
2. Description of Related Art
A frequency response of a radio frequency (RF) receiver or receiving system often is measured or characterized by applying an RF input signal R(f) to an input of the receiver and measuring an intermediate frequency (IF) output signal I(f) produced by the receiver at an IF output. The frequency response or transfer function is a complex ratio of output signal I(f) over the input signal R(f) as a function of frequency f. Moreover, since in most such RF receiver systems an IF portion of the receiver tends to dominate the overall transfer function of the system, the measured frequency response is essentially an IF frequency response of the receiver and may be, in general, represented by a ‘filter-like’ transfer function HI(f). Thus, a frequency response measurement of the receiver system is often essentially an IF frequency response measurement or IF characterization of the receiver system.
Typical approaches to receiver system measurement generally assume that the input signal R(f) is known exactly or at least with sufficiently high precision to support a particular error budget for the measurement. Unfortunately however, in many practical situations complete or precise knowledge of the input signal R(f) may be lacking. This is especially true when attempting to perform highly precise characterizations of downconverting receivers such as a modem measurement receiver or a vector spectrum analyzer. Errors or uncertainties in knowledge of the input signal R(f) contribute to an overall measurement error in the receiver transfer function.
Accordingly, it would be advantageous to have an IF frequency response characterization for an RF receiver that compensates for or effectively reduces an effect that an uncertainty in knowledge of the input signal R(f) has on the characterization. Such an IF frequency response characterization would solve a long-standing need in the area of RF receiver measurement.